vc4: Allow dead code elimination of unused varyings.

total instructions in shared programs: 39022 -> 37341 (-4.31%)
instructions in affected programs:     26979 -> 25298 (-6.23%)
total uniforms in shared programs: 11242 -> 10523 (-6.40%)
uniforms in affected programs:     5836 -> 5117 (-12.32%)

1 files changed, 15 insertions, 0 deletions

diff --git a/src/gallium/drivers/vc4/vc4_program.c b/src/gallium/drivers/vc4/vc4_program.c
index 01941f88428..0674e4fd01a 100644
--- a/src/gallium/drivers/vc4/vc4_program.c
+++ b/src/gallium/drivers/vc4/vc4_program.c
@@ -2018,6 +2018,18 @@ vc4_get_compiled_shader(struct vc4_context *vc4, enum qstage stage,
 
         shader->program_id = vc4->next_compiled_program_id++;
         if (stage == QSTAGE_FRAG) {
+                bool input_live[c->num_input_semantics];
+                struct simple_node *node;
+
+                memset(input_live, 0, sizeof(input_live));
+                foreach(node, &c->instructions) {
+                        struct qinst *inst = (struct qinst *)node;
+                        for (int i = 0; i < qir_get_op_nsrc(inst->op); i++) {
+                                if (inst->src[i].file == QFILE_VARY)
+                                        input_live[inst->src[i].index] = true;
+                        }
+                }
+
                 shader->input_semantics = ralloc_array(shader,
                                                        struct vc4_varying_semantic,
                                                        c->num_input_semantics);
@@ -2025,6 +2037,9 @@ vc4_get_compiled_shader(struct vc4_context *vc4, enum qstage stage,
                 for (int i = 0; i < c->num_input_semantics; i++) {
                         struct vc4_varying_semantic *sem = &c->input_semantics[i];
 
+                        if (!input_live[i])
+                                continue;
+
                         /* Skip non-VS-output inputs. */
                         if (sem->semantic == (uint8_t)~0)
                                 continue;